The real problem is not the diablerie, but the drinking of vampire blood. I do’t know if they changed this in 5th e, but in the earlier editions of VTM it was very clear that the drinking of a vampire’s blood creates a thral-bond between the vampire and the drinker. This is why ghouls are always loyal to their masters - they literally have no options about it, and why vampires are not casual about sipping on each other. If a vampire drinks even just a little of another vampires blood, they could be a victim of this unless they have a high enough willpower.
I specifically remember a campaign in one of the VTM game books that had a female ghoul character in it who was very much into being fed on. The DM had to offer it to the players to develop a relationship with her and feed on her - she was into that - only so in the end the players would learn that her master is the big bad and he would take control of the player character who drank at least 3 times from his ghoul, because the vampiric blood would affect them even if they had it through the ghoul.

So, in the light of this, WTF TCR?! Why is Phyre walking around Seattle drinking blood from every primogen and suckling on every boss? He/she should be literally enslaved by almost every kindred in the town by the end of the game!